In General Packet Radio Service (GPRS) systems, packet control units implement the GPRS air interface protocol. PCUs are typically located remotely from the base transceiver stations (BTSs), usually at a base station controller (BSC) or mobile switching center (MSC) location. Constant and very low delay backhaul is required between a PCU and BTS to allow the PCU to transfer radio link control (RLC) blocks in real time over the air interface via the BTS. This backhaul is typically implemented as leased E1 lines and is usually very expensive to the operator.
In GPRS, this backhaul was pre-existing as long as air interface timeslots were switchable between circuit switched and GPRS service and there was no additional backhaul cost to the operator. However, with the advent of the Enhanced Data for GSM Evolution (EDGE) protocol for GPRS, also known as EGPRS, with data rates up to 59.2 Kbps per air interface timeslot, roughly 4× backhaul per air timeslot is required. This additional backhaul requirement for EDGE represents a very large ongoing cost for operators.
Existing “TRAU” backhaul is low delay and constant delay but is inefficient. (Strictly speaking TRAU frames are Transcoder/Rate Adaptor Unit frames, but “TRAU” is used herein to also encompass frames conveyed between a channel coder and PCU, since such frames are formatted in a similar fashion to Transcoder/Rate Adaptor Unit frames.) Existing “TRAU” backhaul wastes bandwidth by packing variable length (˜30 octet to ˜160 octet) RLC blocks into 160 octet, fixed-length TRAU frames. In contrast, packet backhaul is efficient and low delay but not constant delay. Furthermore, asynchronous transfer mode (ATM) backhaul may be efficient and low delay but not constant delay, or ATM backhaul may be low delay and constant delay but inefficient (depending upon the adaptation layer and data packing used). Generally, then, voice over packet/ATM systems are efficient and approximately constant delay but involve some additional delay over existing “TRAU” backhaul. However, this additional delay is intolerable to the GPRS protocol performance and is very difficult to keep small with the highly variable packet lengths of GPRS.
Therefore, a need exists for an apparatus and method of dynamically managing backhaul resources in order to lower the backhaul costs for EDGE operators while maintaining the low delay and constant delay characteristics required to support remote PCU location.